Just as in a marriage, there are critical milestones. The five major stress-points are:

• Change of circumstances: one of you gets divorced, remarries or has a baby.
• You grow apart from each other: one of you moves house to a different area, becomes more involved in her career or takes up new interests.
• The relationship becomes unbalanced: this happens when one of you is in need of more support than the other can give, or is prepared to give.
• Conflict over partners: one of you doesn’t like the man in the other one’s life.
• New friends: jealousy and misunderstandings arise if one of you becomes attached to a new set of people or starts seeing someone special.

Now, here are the ways on how to be honest tactfully with your best friend:

• Choose the right time, when she’s in a positive frame of mind.
• Choose the right place, with some privacy.
• Avoid alcohol. You’re likely to say the wrong thing in the wrong way after a few drinks, and she’s more likely to overreact.
• Prepare what you want to say beforehand – and be specific about what you’re recommending.
• Be prepared to back up your views and offer support or even practical suggestions.
• Admit you are worried that she will get angry with you for trying to be honest and have been agonizing about exactly how to tell her.
• Choose your words carefully and try to focus on your feelings. There’s a big difference between saying: ‘You always let me down’ and ‘I sometimes feel let down.’
• If it is an aspect of your friend’s behavior that’s making you unhappy, be careful to criticize the behavior, not the person – for example: ‘I feel really hurt when you flirt with my boyfriend’ is far better than ‘I really hate you when you flirt with him.’
• Don’t make accusations or bring up past grievances.
• Be prepared to acknowledge that you may have faults too, and be willing to listen to criticism.
• Be prepared for strong emotions. She may not wish to discuss the problem with you. She may want time on her own before she responds.
• Follow up your meeting with a gesture of support – phone call, a bunch of flowers, a card.
• Ideally, don’t wait until resentments build up. Give each other the chance to air grievances regularly or make suggestions for changes and improvements.

But what if she hasn’t asked for advice? Will she really thank you for saying that she has no dress sense just before she goes to an important interview? And what would her reaction be if you pointed out that she’s drinking too much, her partner’s been unfaithful or that you’re sick of her moaning?

Before you say what you really think, these are the questions you should ask yourself:

• Are you sure about your motives? – Maybe your friend has always been one who gives advice and you can’t resist turning the tables? Have you discovered something secret that’s made you feel wonderful?
• Is it any of your business? – Consider the kind of relationship you have. You may be good friends, but are there no-go areas? Think carefully before you break unwritten rules. For example, if you both know that the one thing you don’t do is criticize the way you run your homes, then steer clear of the subject. But just because she’s always revealed the most intimate details of her sex life, doesn’t necessarily mean she’ll take kindly to unasked-for-advice.
• Will she give you a fair hearing? – There’s no point in a heart-to-heart if she’s so upset by a situation she’ll take everything the wrong way. Maybe it would be wiser to choose a moment when you sense she’s more receptive.
• Are you sure of your facts? – Perhaps the women you saw your friend’s husband kissing on the cheek is his sister or cousin. And double-check any gossip from so-called concerned mutual friends.
• Is this just a difference of opinion? – Think about what you’ll really achieve by speaking out. Will your friend’s life improve; will she be happier? Does she really need to take your comments about, say, her drinking, on board? What you think is too much alcohol may seem very little to her.
• What’s the likely outcome? – You should have a good idea how she’ll react. If you know she’ll ignore your advice, why risk your friendship? For instance, if you know for certain she won’t end an affair; maybe it’s better to offer unconditional support.
• Are you prepared for the worst? – You may feel you couldn’t live with your conscience if you don’t speak out. But you still need to consider how you’ll both feel if your honesty ends up ruining the relationship. Ask yourself whether principles are worth more than the friendship.